CA2072890C - Improved efficiency screen plate for screening pulp - Google Patents
Improved efficiency screen plate for screening pulpInfo
- Publication number
- CA2072890C CA2072890C CA002072890A CA2072890A CA2072890C CA 2072890 C CA2072890 C CA 2072890C CA 002072890 A CA002072890 A CA 002072890A CA 2072890 A CA2072890 A CA 2072890A CA 2072890 C CA2072890 C CA 2072890C
- Authority
- CA
- Canada
- Prior art keywords
- screen
- screen plate
- basket
- undulations
- screening apparatus
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 238000012216 screening Methods 0.000 title claims abstract description 30
- 239000000463 material Substances 0.000 claims abstract description 19
- 229920001131 Pulp (paper) Polymers 0.000 claims description 6
- 238000003754 machining Methods 0.000 abstract description 4
- 238000000034 method Methods 0.000 description 10
- 230000015572 biosynthetic process Effects 0.000 description 5
- 239000013055 pulp slurry Substances 0.000 description 5
- 239000002002 slurry Substances 0.000 description 4
- 238000005520 cutting process Methods 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 238000004080 punching Methods 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 101000997784 Cucurbita maxima Trypsin inhibitor 1 Proteins 0.000 description 1
- 230000000712 assembly Effects 0.000 description 1
- 238000000429 assembly Methods 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000010349 pulsation Effects 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
- D21D5/02—Straining or screening the pulp
- D21D5/16—Cylinders and plates for screens
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
- B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
- B01D29/111—Making filtering elements
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
- B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
- B01D29/13—Supported filter elements
- B01D29/23—Supported filter elements arranged for outward flow filtration
- B01D29/232—Supported filter elements arranged for outward flow filtration with corrugated, folded or wound sheets
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
- B01D29/50—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with multiple filtering elements, characterised by their mutual disposition
- B01D29/52—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with multiple filtering elements, characterised by their mutual disposition in parallel connection
- B01D29/54—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with multiple filtering elements, characterised by their mutual disposition in parallel connection arranged concentrically or coaxially
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
- B01D29/76—Handling the filter cake in the filter for purposes other than for regenerating
- B01D29/86—Retarding cake deposition on the filter during the filtration period, e.g. using stirrers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
- B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
- B07B1/18—Drum screens
Abstract
An improved efficiency screen plate (10) for screening pulp in a pressure screening apparatus (8) is disclosed wherein var-ious design parameters are established which increase screen performance, particularly in screening medium consistency pulp.
The basket is formed of thin, sheet-like material formed without machining into an undulating pattern. Undulation frequencies, slot location, turbulence bar frequency, and turbulence bar height are established for increasing screen performance.
The basket is formed of thin, sheet-like material formed without machining into an undulating pattern. Undulation frequencies, slot location, turbulence bar frequency, and turbulence bar height are established for increasing screen performance.
Description
WO91/10~8 (1) 2 ~ 7~ ~ ,8 9 PCT/US90/07138 -- TITLE
IMPROVED EFFICIENCY SCREEN PLATE FOR SCREENING PULP
BACKGROUND OF THE INVENTION
i. Technical Field The present invention pertains to improvements in pulp screening apparatus and pertains particularly to an improved efficiency screen basket for use in pressure screens wherein the basket configuration provides a higher level of efficiency than existing designs.
ii. Prior Art In the papermaking process, screens are used to separate acceptable papermaking fiber from unacceptable constituents of a slurry of pulp fiber, in preparing the pulp slurry to be made into paper. In typical wood pulp screens, a slurry of pulp flows through a perforate, cylindrical screen plate or basket which may be smooth, or which may have a contoured surface facing toward the stock flowing through the screen, to increase the effective screening area. It is known to utilize different hole, slot or hole and slot combinations for optimizing screening performance.
To aid in passing the acceptable pulp through the screen plate, and to reduce plugging, pulsations are generated in the slurry, such as by passing a hydrofoil-shaped member past the screen plate. It is also known to use blunt, turbulence generating members on a screen rotor, to agitate the stock near the screen surface and improve screening efficiency. Such rotors generally operate effectively to screen pulp at one percent to two percent consistency, but do not work effectively at higher consistencies. U.S. Patent 4,855,038 discloses a pulp screen rotor which generates both turbulence and pulse and WO 91/10008 /A) 2 0 7 2 a 9 PCT!us9o~o7l38 _ has been found to work effectively at three percent to four percent consistencies and higher. In many applications, the higher consistencies, referred to as medium consistency, are preferred for process reasons.
To provide sufficient strength to the screen plate, which generally is a basket-shaped member surrounding the rotor, to withstand the pressure experienced in the pressurized screen, and to increase the screening capacity by presenting increased screening area, it has been the accepted practice in all pressure pulp screens to provide a thickly-walled screen plate which is machined to present the desired surface. Such machining is a time-consuming and expensive process. As a result of the manufacturing restrictions in the machining process, which are imposed at ieast in part by limitations of the machine tools themselves, the total available open accepts flow area in the screen plate has been limited, and the final shape of the screen plate has been a compromise between the limitations of machining znd the desired optimum screening shape.
Since the machined screen plates are a single, inte~ral piece, wear or damage in a small area has required replacement of the entire screen plate; including the screening surfaces, mounting surfaces, and support members.
When the wear or damage occurs prematurely, the expense of operating such a screen increases significantly.
In co-pending ~pplication Wo 89/12137, a modular screen basket is disclosed wherein relatively thin, sheet-like material is formed into the desired shape or contour.
Stamping, pressing, and bending techniques are taught to form the screen plate, which does not require mach;n;ng.
The holes or slots are taught to be created during, before, or after formation o~ the undulations in the sheet-like material, with suggested forming techniques including laser beam cutting and punching. Utilizing a punch die as part of the WO 91/10008 (3/A) 20728 ~ T/US90/07138 , forming process is suggested as a simplified, cost-effective manner for forming the openings. The modular basket has sufficient strength for pressure screening applications, including medium consistency screening.
In co-pending Wo 89/12137, it is suggested that numerous different undulating configurations, slot and hole com~inations and other features can be utilized. The basket forming technique disclosed in WO 89/12137 allows greater control of formation, both of the undulating surface and of the slot or hole openings. It has now been discovered that if various parameters are followed with respect to the physical characteristics of the basket, the basket will operate more efficiency, resulting in optimum screen performance, even at higher consistencies.
BACKGROUND OF T~E INVENTION
It is, therefore, one of the primary objects of the present invention to provide an improved efficiency screen plate for screening pulp in a pressurized screening apparatus.
Another cbject of the present invention is to provide design parameter for physical features in a screen basket resulting in optimum screen~performance.
Still another object of the present invention is to provide an optimized screen basket for improving screen performance when medium consistency slurries are processed.
These and other objects are achieved in the present invention by providing a screen basket made of thin, sheet-like material formed into an undulating pattern, and provided with slot openings for the passage of pulp. Two or less undulations 2re provided per centimeter of basket circumference, and the slot openings are provided at top dead inside center of the undulation, plus 90 degrees to the direction of flow. Turbulence bars are WO 91/10008 (4/A) 2 0 7 2 89 ~ T/US90~07138 provided in at least every third undulation, which turbulence bars protrude above the undulations no more than about .475 cm.
Further ob~ects and advantages will be apparent from the following detailed description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view, with portions broken away, illustratins a pulp screen structure utilizing a modular screen basket made of thin-walled material manufactured according to the present invention, to provide improved screening efficiency.
Figure 2 is an enlarged fragmentary sectional view taken substantially along line IT--I of Figure 1.
Figure 3 is an enlarged cross-sectional view of a portion of screen basket shown in the previous figures, which has been constructed in accordance with the design parameters of the present invention, to result in increased screen efficiency.
Figure is a graph illustrating test results performed with screen baskets of various corrugation frequencies.
Figure 5 is a graph illustrating test results from tests conducted on baskets having various slot locations.
Figures 6, 7 and 8 illustrate screen baskets having, respectively, slot locations at zero degrees, plus 30 degrees, and plus 4~ degrees.
Figure 9 is a graph illustrating the results of tests conducted on baskets having various turbulence bar locations.
WO 91/10008 (5/A) PCT/US~0/07138 -Figure 10 is a graph illustrating test results conducted on baskets having various turbulence bar heights.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now more specifically to the drawings, and to Figure 1 in particular, numeral 8 designates a screening apparatus wherein previously treated pulp is screened to remove foreign elements such as shives, bark, knots, dirt, glass, plastic, and the like. A screen plate assembly is shown at 10, and defines in the apparatus 8 an interior chamber 11 where the pulp slurry to be screened enters the apparatus and an exterior chamber 12 where the screened pulp slurry flows out of the apparatus after passing through the screen plate assembly. The assembly is enclosed in a housing 13 which includes an end plate 13a secured by bolts 13b. The housing has 2n inlet, not shown, for admitting pulp into the interior chamber 11, and an outlet, not shown, leading from the chamber 11 for the foreign material to flow out of the apparatus, which foreign material has not passed through the screen plate assembly 10 from the interior chamber 11 to the exterior chamber 12. The accepted pulp, which has flowed from the interior chamber 11 through the screen plate assembly 10 to the exterior chamber 12, flows out of the screen apparatus 8 through the accepts outlet 14.
The screen plate assembly 10 is stationary within the housing 13, and a rotor 18 is mounted for rotation within the cylindrical screen plate assembly, for aiding passage of the pulp slurry through the screen plate, and to help inhibit plugging. The rotor is rotational about a rotary-driven shaft 19 which rotates in a clock-wise direction, as viewed in Figure 1. The rotor shown is merely illustrative of a suitable type, and it should be understood that the present invention can be used for screen plates of various types for various pulse, turbulence, and combination pulse and turbulence generating rotors, particularly those most suitable for medium consistency screening.
WO9l/10~8 (6) PCT/US90/07138 ,;
The screen plate assembly 10 includes cylindrical screen sections 16 and 17 which, without support, are essentially flexible and would not withstand normal screen pressures. The screen sections, therefore, require rigidifying or strengthening for use in the pressurized environment of screen apparatus 8. The necessary support and strengthening is provided by end rings-20 and 20a, and an intermediate support ring 21. Each of the rings has grooves, such as illustrated by the grooves 23 and 24 in the ring 21 shown in Figure 2. The grooves 23 and 24 are circular, to hold the screen sections in a substantially cylindrical shape. The grooves 23 and 24 have a radial dimension substantially equal to the radial thickness of the shaped screen plates.
The screen plates are formed from relatively thin, sheet-like material compared to the heretofore known machined screen plates. The thin material is formed into various shapes or contours, generally undulated, so as to present a substantial amount of screening area to the stock.
During assembly, each of the shaped screen plates is positioned into the grooves in the end rings 20 or 20a and the intermediate ring 21, and the rings are pulled together to force the screen plates into the grooves. For this purpose, axially extending rods 22 are provided, spaced circumferentially from each other, and the rods are provided at their ends with threads and nuts 22a, so that the nuts can be tightened to pull the end rings towards each other and force the ends of the screen plates into the grooves.
The grooves are preferably tapered so that the slot becomes narrower in an inward direction toward the bottom of the groove. When the rods are tightened, the screen plates are pushed tightly into the tapered grooves, so that the screen plates are held firmly in a fixed position circumferentially. It should be recognized that the screen assemblies can be made of different lengths, longer or shorter, or even greater in number, and additional WO 91/10008 207 289~7/A! PCT/rJS~0/07138 --reinforcing intermediate rings, such as 21, may be employed between the ends of each of the adjacent screens.
Screen openings such as holes 25 or slots 26, as shown in Figure 2, extend through the thin screen material, providing a path from the interior chamber 11 to the exterior chamber 12. In accordance with the present invention, the elongated slot-like openings are used. For elongated openings, such as slots 26, material of about .122 cm thickness can be used. It will be recognized that, depending of the formation technique utilized, other sheet thicknesses may be employed.
The thin material of the screen sections may be stainless steel or similar sheet material which is formed in a generally cylindrical shape having undulations extending around the circumference of the screen. In a simplified form, the undulations may take the form cf a series of upright and ~nverted U-shaped sections 27 and 28, or, in other words, the screen essentially consists of a series of deep corrugations. An undulation height of about 1.143 cm has been found to be acceptable. A suitable apparatus and method for forming the corrugations can be found in co-pending WO 89/12137.
As taught therein, the shape or pattern formed can be changed by modifyin~ the shape of the forming tool used, and the thin, sheet-like material can be readily shaped or formed into the desLred pattern, with the slot opening being accurately located with a punching or lancing tool utilized in conjunction with the forming process, or by laser beam cutting. When slots are formed, coining or prestressing at the ends of the slo~s may be used to m; n;m; ze crack formation an~ propa~ation, thereby increasing the wear life of the basket.
The modular screen basket of formed, thin, sheet-like material has made a~ailable a great variety of basket configurations, including the location of openings. It has 2 0 7 2 8 9 0 (8/A) PCT/US~0/07138 .
now been discovered that, within certain parameters for slot location, corrugation frequency and the like, an increase in overall screen operation efficiency can be realized, particularly in screening medium consistency pulp slurry.
Screen performance is greatly enhanced when the design parameters are followed.
In forming the corrugations or undulations with the thin, sheet-like material, it is possible to form the corrugations spaced relatively closely together or relatively far apart. All that ls required is the proper formation tool. It has been found, however, that baskets having more than two undulations or corrugations per circumferential centimeter of the basket result in reduced screen capacity. Therefore, the thin, sheet-like material should be formed with two or less corrugations per centimeter, and preferably at one and two-tenths corrugations per centimeter. In a basket operated with the rotor of U.S. Patent 4,855,038 on pulp at four percent consistency, two and four-tenths corrugations per centimeter yielded a capacity o~ approximately 120 tons per day, while two corrugations per centimeter yielded a capacity of approximately 185 tons per day. One and two-tenths corrugations per centimeter yielded a capacity of 275 tons per day. The results of these tests are shown in the graph of Figure 4.
Utili2ing the preferred corrugation frequency of one and two-tenths corrugations per centimeter, further tests were run with the sa~e rotor to determine the optimum slot location. The resul.s of these tests are indicated in Figure 5. From these tests, it has been determined that the slot openings should be provided on the inside of the basket, that is on the corrugations or ridges closest to the rotor. In the graph of Figure 5, zero degrees refers to that location at top dead center of the corrugations nearest the rotor, as illust~ated in Figure 6, and +180 degrees indicates the bottom dead center in the trough or corrugation farthest from the rotor. At zero degrees or top WO 91/10008 207289 (8/B) ~T/TJS40/07138 `' dead center, the screen capacity was approximately 60 tons per day, while at 180 degrees or bottom dead center, WO 91/10008 2 0 7 2 8 9 0 (9/A/1) PCT/JS30fO7138 .
capacity was 50 tons per day. At +30 degrees, which is 30 degrees downstream from the top dead center location, as shown in Figure 7, the screen capacity was 180 tons per day.
At +45 degrees, which is 45 degrees downstream from top dead center, as illustrated in Figure 8, screen capacity was approximately 220 tons per day. Thus, slot location at +45 degrees is preferred, and the optLmum range is from O to +45 degrees.
It was further discovered that the use of turbulence or wear bars can increase screen capacity. Figure 9 illustrates the results of tests run to determine the preferred number of turbulence bars, when screening four percent pulp. When no turbulence bars were utilized, screen capacity was approximately 210 tons per day. When one turbulence bar was provided in every ninth corrugation, the screen capacity was 225 ~ons per day. When one turbulence ~c- ~as provided in every fif t;. corrugation, screen capacity was 270 tons per day. When one turbulence bar was provided in each third corrugation, a capacity of 270 tons per day was also experienced.
The effect of turbulence bar height was also investigated, and Figure 10 displays in graphic form those results. The tests were again conducted with the rotor of U.S. Patent ,855,038 in a screen having about 1.25 cm rotor-to-basket spacing. Medium consistency pulp was used.
When the turbulence bar was in height equal to the depth of the corrugation in which it was placed, screen capacity was approximately 215 tons per day. When the turbulence bar was provided to extend above the corrugation by .318 cm, the screen capacity increased to 250 tons per day. However, when the turbulence bar was provided to extend above the corrugation by .63S cm, screen capacity dropped to 120 tons per day.
20~2890 WO 91/10008 (10/A) PCT/-JS30tO7138 , Figure 3 illustrates a preferred basket arrangement.
The basket includes a series of undulations or corrugations having rotor side peaks 27 closest to the rotor, and valleys 28 farthest away. The corrugations are provided at a fre~uency of less than two corrugations per centimeter of basket circumference. Turbulence bars 50 are provided in every third corrugation, and project above the corrugations a distance 52 no more than about .475 cm. Slots 26 are provided oriented 45 degrees in the downstream direction from top dead center of the corrugation.
An optimized screen basket configuration has been shown and described in detail herein. It should be recognized, however, that various changes may be made without departing from the scope of the present invention.
IMPROVED EFFICIENCY SCREEN PLATE FOR SCREENING PULP
BACKGROUND OF THE INVENTION
i. Technical Field The present invention pertains to improvements in pulp screening apparatus and pertains particularly to an improved efficiency screen basket for use in pressure screens wherein the basket configuration provides a higher level of efficiency than existing designs.
ii. Prior Art In the papermaking process, screens are used to separate acceptable papermaking fiber from unacceptable constituents of a slurry of pulp fiber, in preparing the pulp slurry to be made into paper. In typical wood pulp screens, a slurry of pulp flows through a perforate, cylindrical screen plate or basket which may be smooth, or which may have a contoured surface facing toward the stock flowing through the screen, to increase the effective screening area. It is known to utilize different hole, slot or hole and slot combinations for optimizing screening performance.
To aid in passing the acceptable pulp through the screen plate, and to reduce plugging, pulsations are generated in the slurry, such as by passing a hydrofoil-shaped member past the screen plate. It is also known to use blunt, turbulence generating members on a screen rotor, to agitate the stock near the screen surface and improve screening efficiency. Such rotors generally operate effectively to screen pulp at one percent to two percent consistency, but do not work effectively at higher consistencies. U.S. Patent 4,855,038 discloses a pulp screen rotor which generates both turbulence and pulse and WO 91/10008 /A) 2 0 7 2 a 9 PCT!us9o~o7l38 _ has been found to work effectively at three percent to four percent consistencies and higher. In many applications, the higher consistencies, referred to as medium consistency, are preferred for process reasons.
To provide sufficient strength to the screen plate, which generally is a basket-shaped member surrounding the rotor, to withstand the pressure experienced in the pressurized screen, and to increase the screening capacity by presenting increased screening area, it has been the accepted practice in all pressure pulp screens to provide a thickly-walled screen plate which is machined to present the desired surface. Such machining is a time-consuming and expensive process. As a result of the manufacturing restrictions in the machining process, which are imposed at ieast in part by limitations of the machine tools themselves, the total available open accepts flow area in the screen plate has been limited, and the final shape of the screen plate has been a compromise between the limitations of machining znd the desired optimum screening shape.
Since the machined screen plates are a single, inte~ral piece, wear or damage in a small area has required replacement of the entire screen plate; including the screening surfaces, mounting surfaces, and support members.
When the wear or damage occurs prematurely, the expense of operating such a screen increases significantly.
In co-pending ~pplication Wo 89/12137, a modular screen basket is disclosed wherein relatively thin, sheet-like material is formed into the desired shape or contour.
Stamping, pressing, and bending techniques are taught to form the screen plate, which does not require mach;n;ng.
The holes or slots are taught to be created during, before, or after formation o~ the undulations in the sheet-like material, with suggested forming techniques including laser beam cutting and punching. Utilizing a punch die as part of the WO 91/10008 (3/A) 20728 ~ T/US90/07138 , forming process is suggested as a simplified, cost-effective manner for forming the openings. The modular basket has sufficient strength for pressure screening applications, including medium consistency screening.
In co-pending Wo 89/12137, it is suggested that numerous different undulating configurations, slot and hole com~inations and other features can be utilized. The basket forming technique disclosed in WO 89/12137 allows greater control of formation, both of the undulating surface and of the slot or hole openings. It has now been discovered that if various parameters are followed with respect to the physical characteristics of the basket, the basket will operate more efficiency, resulting in optimum screen performance, even at higher consistencies.
BACKGROUND OF T~E INVENTION
It is, therefore, one of the primary objects of the present invention to provide an improved efficiency screen plate for screening pulp in a pressurized screening apparatus.
Another cbject of the present invention is to provide design parameter for physical features in a screen basket resulting in optimum screen~performance.
Still another object of the present invention is to provide an optimized screen basket for improving screen performance when medium consistency slurries are processed.
These and other objects are achieved in the present invention by providing a screen basket made of thin, sheet-like material formed into an undulating pattern, and provided with slot openings for the passage of pulp. Two or less undulations 2re provided per centimeter of basket circumference, and the slot openings are provided at top dead inside center of the undulation, plus 90 degrees to the direction of flow. Turbulence bars are WO 91/10008 (4/A) 2 0 7 2 89 ~ T/US90~07138 provided in at least every third undulation, which turbulence bars protrude above the undulations no more than about .475 cm.
Further ob~ects and advantages will be apparent from the following detailed description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view, with portions broken away, illustratins a pulp screen structure utilizing a modular screen basket made of thin-walled material manufactured according to the present invention, to provide improved screening efficiency.
Figure 2 is an enlarged fragmentary sectional view taken substantially along line IT--I of Figure 1.
Figure 3 is an enlarged cross-sectional view of a portion of screen basket shown in the previous figures, which has been constructed in accordance with the design parameters of the present invention, to result in increased screen efficiency.
Figure is a graph illustrating test results performed with screen baskets of various corrugation frequencies.
Figure 5 is a graph illustrating test results from tests conducted on baskets having various slot locations.
Figures 6, 7 and 8 illustrate screen baskets having, respectively, slot locations at zero degrees, plus 30 degrees, and plus 4~ degrees.
Figure 9 is a graph illustrating the results of tests conducted on baskets having various turbulence bar locations.
WO 91/10008 (5/A) PCT/US~0/07138 -Figure 10 is a graph illustrating test results conducted on baskets having various turbulence bar heights.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now more specifically to the drawings, and to Figure 1 in particular, numeral 8 designates a screening apparatus wherein previously treated pulp is screened to remove foreign elements such as shives, bark, knots, dirt, glass, plastic, and the like. A screen plate assembly is shown at 10, and defines in the apparatus 8 an interior chamber 11 where the pulp slurry to be screened enters the apparatus and an exterior chamber 12 where the screened pulp slurry flows out of the apparatus after passing through the screen plate assembly. The assembly is enclosed in a housing 13 which includes an end plate 13a secured by bolts 13b. The housing has 2n inlet, not shown, for admitting pulp into the interior chamber 11, and an outlet, not shown, leading from the chamber 11 for the foreign material to flow out of the apparatus, which foreign material has not passed through the screen plate assembly 10 from the interior chamber 11 to the exterior chamber 12. The accepted pulp, which has flowed from the interior chamber 11 through the screen plate assembly 10 to the exterior chamber 12, flows out of the screen apparatus 8 through the accepts outlet 14.
The screen plate assembly 10 is stationary within the housing 13, and a rotor 18 is mounted for rotation within the cylindrical screen plate assembly, for aiding passage of the pulp slurry through the screen plate, and to help inhibit plugging. The rotor is rotational about a rotary-driven shaft 19 which rotates in a clock-wise direction, as viewed in Figure 1. The rotor shown is merely illustrative of a suitable type, and it should be understood that the present invention can be used for screen plates of various types for various pulse, turbulence, and combination pulse and turbulence generating rotors, particularly those most suitable for medium consistency screening.
WO9l/10~8 (6) PCT/US90/07138 ,;
The screen plate assembly 10 includes cylindrical screen sections 16 and 17 which, without support, are essentially flexible and would not withstand normal screen pressures. The screen sections, therefore, require rigidifying or strengthening for use in the pressurized environment of screen apparatus 8. The necessary support and strengthening is provided by end rings-20 and 20a, and an intermediate support ring 21. Each of the rings has grooves, such as illustrated by the grooves 23 and 24 in the ring 21 shown in Figure 2. The grooves 23 and 24 are circular, to hold the screen sections in a substantially cylindrical shape. The grooves 23 and 24 have a radial dimension substantially equal to the radial thickness of the shaped screen plates.
The screen plates are formed from relatively thin, sheet-like material compared to the heretofore known machined screen plates. The thin material is formed into various shapes or contours, generally undulated, so as to present a substantial amount of screening area to the stock.
During assembly, each of the shaped screen plates is positioned into the grooves in the end rings 20 or 20a and the intermediate ring 21, and the rings are pulled together to force the screen plates into the grooves. For this purpose, axially extending rods 22 are provided, spaced circumferentially from each other, and the rods are provided at their ends with threads and nuts 22a, so that the nuts can be tightened to pull the end rings towards each other and force the ends of the screen plates into the grooves.
The grooves are preferably tapered so that the slot becomes narrower in an inward direction toward the bottom of the groove. When the rods are tightened, the screen plates are pushed tightly into the tapered grooves, so that the screen plates are held firmly in a fixed position circumferentially. It should be recognized that the screen assemblies can be made of different lengths, longer or shorter, or even greater in number, and additional WO 91/10008 207 289~7/A! PCT/rJS~0/07138 --reinforcing intermediate rings, such as 21, may be employed between the ends of each of the adjacent screens.
Screen openings such as holes 25 or slots 26, as shown in Figure 2, extend through the thin screen material, providing a path from the interior chamber 11 to the exterior chamber 12. In accordance with the present invention, the elongated slot-like openings are used. For elongated openings, such as slots 26, material of about .122 cm thickness can be used. It will be recognized that, depending of the formation technique utilized, other sheet thicknesses may be employed.
The thin material of the screen sections may be stainless steel or similar sheet material which is formed in a generally cylindrical shape having undulations extending around the circumference of the screen. In a simplified form, the undulations may take the form cf a series of upright and ~nverted U-shaped sections 27 and 28, or, in other words, the screen essentially consists of a series of deep corrugations. An undulation height of about 1.143 cm has been found to be acceptable. A suitable apparatus and method for forming the corrugations can be found in co-pending WO 89/12137.
As taught therein, the shape or pattern formed can be changed by modifyin~ the shape of the forming tool used, and the thin, sheet-like material can be readily shaped or formed into the desLred pattern, with the slot opening being accurately located with a punching or lancing tool utilized in conjunction with the forming process, or by laser beam cutting. When slots are formed, coining or prestressing at the ends of the slo~s may be used to m; n;m; ze crack formation an~ propa~ation, thereby increasing the wear life of the basket.
The modular screen basket of formed, thin, sheet-like material has made a~ailable a great variety of basket configurations, including the location of openings. It has 2 0 7 2 8 9 0 (8/A) PCT/US~0/07138 .
now been discovered that, within certain parameters for slot location, corrugation frequency and the like, an increase in overall screen operation efficiency can be realized, particularly in screening medium consistency pulp slurry.
Screen performance is greatly enhanced when the design parameters are followed.
In forming the corrugations or undulations with the thin, sheet-like material, it is possible to form the corrugations spaced relatively closely together or relatively far apart. All that ls required is the proper formation tool. It has been found, however, that baskets having more than two undulations or corrugations per circumferential centimeter of the basket result in reduced screen capacity. Therefore, the thin, sheet-like material should be formed with two or less corrugations per centimeter, and preferably at one and two-tenths corrugations per centimeter. In a basket operated with the rotor of U.S. Patent 4,855,038 on pulp at four percent consistency, two and four-tenths corrugations per centimeter yielded a capacity o~ approximately 120 tons per day, while two corrugations per centimeter yielded a capacity of approximately 185 tons per day. One and two-tenths corrugations per centimeter yielded a capacity of 275 tons per day. The results of these tests are shown in the graph of Figure 4.
Utili2ing the preferred corrugation frequency of one and two-tenths corrugations per centimeter, further tests were run with the sa~e rotor to determine the optimum slot location. The resul.s of these tests are indicated in Figure 5. From these tests, it has been determined that the slot openings should be provided on the inside of the basket, that is on the corrugations or ridges closest to the rotor. In the graph of Figure 5, zero degrees refers to that location at top dead center of the corrugations nearest the rotor, as illust~ated in Figure 6, and +180 degrees indicates the bottom dead center in the trough or corrugation farthest from the rotor. At zero degrees or top WO 91/10008 207289 (8/B) ~T/TJS40/07138 `' dead center, the screen capacity was approximately 60 tons per day, while at 180 degrees or bottom dead center, WO 91/10008 2 0 7 2 8 9 0 (9/A/1) PCT/JS30fO7138 .
capacity was 50 tons per day. At +30 degrees, which is 30 degrees downstream from the top dead center location, as shown in Figure 7, the screen capacity was 180 tons per day.
At +45 degrees, which is 45 degrees downstream from top dead center, as illustrated in Figure 8, screen capacity was approximately 220 tons per day. Thus, slot location at +45 degrees is preferred, and the optLmum range is from O to +45 degrees.
It was further discovered that the use of turbulence or wear bars can increase screen capacity. Figure 9 illustrates the results of tests run to determine the preferred number of turbulence bars, when screening four percent pulp. When no turbulence bars were utilized, screen capacity was approximately 210 tons per day. When one turbulence bar was provided in every ninth corrugation, the screen capacity was 225 ~ons per day. When one turbulence ~c- ~as provided in every fif t;. corrugation, screen capacity was 270 tons per day. When one turbulence bar was provided in each third corrugation, a capacity of 270 tons per day was also experienced.
The effect of turbulence bar height was also investigated, and Figure 10 displays in graphic form those results. The tests were again conducted with the rotor of U.S. Patent ,855,038 in a screen having about 1.25 cm rotor-to-basket spacing. Medium consistency pulp was used.
When the turbulence bar was in height equal to the depth of the corrugation in which it was placed, screen capacity was approximately 215 tons per day. When the turbulence bar was provided to extend above the corrugation by .318 cm, the screen capacity increased to 250 tons per day. However, when the turbulence bar was provided to extend above the corrugation by .63S cm, screen capacity dropped to 120 tons per day.
20~2890 WO 91/10008 (10/A) PCT/-JS30tO7138 , Figure 3 illustrates a preferred basket arrangement.
The basket includes a series of undulations or corrugations having rotor side peaks 27 closest to the rotor, and valleys 28 farthest away. The corrugations are provided at a fre~uency of less than two corrugations per centimeter of basket circumference. Turbulence bars 50 are provided in every third corrugation, and project above the corrugations a distance 52 no more than about .475 cm. Slots 26 are provided oriented 45 degrees in the downstream direction from top dead center of the corrugation.
An optimized screen basket configuration has been shown and described in detail herein. It should be recognized, however, that various changes may be made without departing from the scope of the present invention.
Claims (9)
1. In a screen plate (10) for use in a paper pulp pressure screening apparatus (8) having a rotor (18) operating near one side of the screen plate (10), the plate (10) being a cylindrical screen basket formed of a relatively thin, sheet-like material of substantially uniform thickness therethrough, said material being formed into an undulating shape including a series of corrugations circumferentially around the screen providing inner ridges near the rotor and outer ridges, and having slots defining elongated screen openings (25,26) formed therethrough, the improvement comprising:
said slots being disposed axially in said basket and only on a downstream side from top dead center of inner ridges only; and said undulations being provided at not more than two undulations per circumferential centimeter of basket.
said slots being disposed axially in said basket and only on a downstream side from top dead center of inner ridges only; and said undulations being provided at not more than two undulations per circumferential centimeter of basket.
2. In the improved screen plate (10) as defined in claim 1, the further improvement wherein said undulations are provided at not more than one and two-tenths undulations per circumferential centimeter of basket.
3. The improvement for a screen plate (10) for use in paper pulp pressure screening apparatus (8) as defined in claim 1, in which said openings (25,26) are provided in regions top dead center of the ridges to about 45 degrees downstream from top dead center of the ridges.
4. The improved screen plate (10) for use in paper pulp pressure screening apparatus (8) as defined in claim 1, in which said openings (25,26) are provided at locations approximately 45 degrees from top dead center of the ridges in a downstream direction.
5. In a screen plate (10) for use in paper pulp pressure screening apparatus (8), the improvement as defined in claim 1, in which turbulence bars (50) are provided in at (12/A/1)
6. The improvement for a pressure pulp screening apparatus (8) as defined in claim 5, in which said turbulence bars (50) extend above adjacent peaks of undulations by a dimension not more than about .635 cm.
7. The improvement for a pressure pulp screening apparatus (8) as defined in claim 5, in which said turbulence bars (50) extend above adjacent peaks of undulations by a dimension not more than about .318 cm.
8. The improved screen plate (10) for use in paper pulp pressure screening apparatus (8) as defined in claim 7, in which said openings (25,26) are provided at locations approximately 45 degrees from top dead center of the ridges in a downstream direction.
9. In the improved screen plate (10) as defined in claim 8, the further improvement wherein said undulations are provided at not more than one and two-tenths undulations per circumferential centimeter of basket.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US462,686 | 1990-01-02 | ||
| US07/462,686 US5041212A (en) | 1990-01-02 | 1990-01-02 | Efficiency screen plate for screening pulp |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2072890A1 CA2072890A1 (en) | 1991-07-03 |
| CA2072890C true CA2072890C (en) | 1995-07-18 |
Family
ID=23837395
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002072890A Expired - Fee Related CA2072890C (en) | 1990-01-02 | 1990-12-05 | Improved efficiency screen plate for screening pulp |
Country Status (11)
| Country | Link |
|---|---|
| US (1) | US5041212A (en) |
| EP (1) | EP0509004B1 (en) |
| JP (1) | JPH0742674B2 (en) |
| AU (1) | AU7039291A (en) |
| BR (1) | BR9007966A (en) |
| CA (1) | CA2072890C (en) |
| DE (1) | DE69003953T2 (en) |
| ES (1) | ES2046042T3 (en) |
| FI (1) | FI102090B1 (en) |
| NZ (1) | NZ236690A (en) |
| WO (1) | WO1991010008A1 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE501273C2 (en) * | 1993-05-14 | 1994-12-19 | Knutsilplaotar Ab | Screen drum for sieving suspensions of lignocellulosic fibrous material |
| JPH08209574A (en) * | 1995-01-27 | 1996-08-13 | Aikawa Iron Works Co Ltd | Screen plate for production of paper |
| US5823355A (en) * | 1995-03-29 | 1998-10-20 | Beloit Technologies, Inc. | Fibresaver screen basket support |
| US5791495A (en) * | 1996-03-11 | 1998-08-11 | Beloit Technologies, Inc. | Paper pulp screen cylinder |
| US5954956A (en) * | 1997-07-22 | 1999-09-21 | J&L Fiber Services | Modular screen cylinder and a method for its manufacture |
| WO1999007485A1 (en) * | 1997-08-06 | 1999-02-18 | Thermo Black Clawson Inc. | Paper stock screening apparatus and method |
| DE10065931A1 (en) * | 2000-12-22 | 2002-06-27 | Voith Paper Patent Gmbh | Process for the production of screens which can be used in the wet screening of paper fiber suspensions |
| CA2444486C (en) * | 2001-04-16 | 2013-04-02 | J & L Fiber Services, Inc. | Screen cylinder and method |
| DE102007020325B3 (en) * | 2007-04-30 | 2009-01-15 | Voith Patent Gmbh | Process for producing a screen for the treatment of pulp suspensions suitable for paper production |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE11572C (en) * | A. 'SPRENGER in Stuttgart, Gartenstrafse | Equipment on zithers and guitars to amplify the resonance | ||
| US2068511A (en) * | 1935-07-15 | 1937-01-19 | Municipal Sanitary Service Cor | Filter |
| GB519680A (en) * | 1938-09-22 | 1940-04-03 | James Walker | Improvements in or relating to strainer plates and drums |
| US2311813A (en) * | 1939-08-02 | 1943-02-23 | Erich A Beck | Paper pulp screen |
| US2827169A (en) * | 1954-12-07 | 1958-03-18 | Internat Pulp Products Inc | Screen plate |
| CA1180686A (en) * | 1980-08-25 | 1985-01-08 | Black Clawson Company (The) | Paper making stock screening apparatus incorporating circular apertured cylindrical pressure screen |
| US4855038A (en) * | 1985-06-20 | 1989-08-08 | Beloit Corporation | High consistency pressure screen and method of separating accepts and rejects |
| GB2195911A (en) * | 1986-10-08 | 1988-04-20 | Ingersoll Rand Co | Screening apparatus for pulp |
| US4954249A (en) * | 1988-06-10 | 1990-09-04 | Beloit Corporation | Wave screen plate |
-
1990
- 1990-01-02 US US07/462,686 patent/US5041212A/en not_active Expired - Fee Related
- 1990-12-05 EP EP91901387A patent/EP0509004B1/en not_active Expired - Lifetime
- 1990-12-05 WO PCT/US1990/007138 patent/WO1991010008A1/en active IP Right Grant
- 1990-12-05 JP JP3501773A patent/JPH0742674B2/en not_active Expired - Lifetime
- 1990-12-05 DE DE91901387T patent/DE69003953T2/en not_active Expired - Fee Related
- 1990-12-05 CA CA002072890A patent/CA2072890C/en not_active Expired - Fee Related
- 1990-12-05 AU AU70392/91A patent/AU7039291A/en not_active Abandoned
- 1990-12-05 BR BR909007966A patent/BR9007966A/en not_active IP Right Cessation
- 1990-12-05 ES ES91901387T patent/ES2046042T3/en not_active Expired - Lifetime
-
1991
- 1991-01-04 NZ NZ236690A patent/NZ236690A/en unknown
-
1992
- 1992-07-01 FI FI923059A patent/FI102090B1/en active
Also Published As
| Publication number | Publication date |
|---|---|
| US5041212A (en) | 1991-08-20 |
| FI102090B (en) | 1998-10-15 |
| DE69003953T2 (en) | 1994-04-07 |
| EP0509004B1 (en) | 1993-10-13 |
| JPH0742674B2 (en) | 1995-05-10 |
| BR9007966A (en) | 1992-10-13 |
| WO1991010008A1 (en) | 1991-07-11 |
| NZ236690A (en) | 1993-08-26 |
| EP0509004A1 (en) | 1992-10-21 |
| AU7039291A (en) | 1991-07-24 |
| ES2046042T3 (en) | 1994-01-16 |
| DE69003953D1 (en) | 1993-11-18 |
| FI923059A0 (en) | 1992-07-01 |
| CA2072890A1 (en) | 1991-07-03 |
| FI923059A (en) | 1992-07-01 |
| FI102090B1 (en) | 1998-10-15 |
| JPH05504382A (en) | 1993-07-08 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| AU631557B2 (en) | Wave screen plate and manufacturing methods | |
| US5139154A (en) | Wear screen plate and method of manufacture thereof | |
| US5147543A (en) | Rotating element for a screening apparatus with a contour surface produced by a plurality of protrusions in the direction of the axial length of the cylindrical rotor | |
| CA2072890C (en) | Improved efficiency screen plate for screening pulp | |
| CA2118410C (en) | Apparatus for treating fiber suspension | |
| US5023986A (en) | Method of manufacturing a wave screen plate | |
| US3586172A (en) | Screening apparatus | |
| CN101105014B (en) | Pulp-breaking machine extraction bedplate for fiber separation for paper pulp | |
| US7188733B2 (en) | Screening device, such as a screen cylinder, and method of manufacture of the screening device | |
| US5041214A (en) | Wave screen plate | |
| CA2067108C (en) | Basket profile for screens | |
| JP4530545B2 (en) | Filter apparatus and method for filtration of paper pulp | |
| US4105543A (en) | Method for screening paper fiber stock | |
| US5285560A (en) | Method for repairing a screen plate assembly | |
| EP0651091A1 (en) | Finely perforated undulating screen cylinder | |
| EP1184509B2 (en) | Screening apparatus for fiber suspension | |
| US5249734A (en) | Rotor disc for a refiner and method of formation thereof | |
| NZ247209A (en) | Undulating screen plate with screen openings: turbulence bar disposed at every fifth undulation | |
| EP0119345A1 (en) | Screening apparatus for paper making stock | |
| US5047118A (en) | Method for decreasing energy consumption during refining of fiber material at a reduced grinding frequency while maintaining capacity | |
| EP3023541B1 (en) | Papermaking strainer and manufacturing method of papermaking strainer | |
| CA1306378C (en) | Method for decreasing energy consumption during refining of fiber material while maintaining capacity |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |